Stabilized white oil



Patented Feb. 8, 1944 STABILIZED on.

Francis m. Archibald, Elisabeth, N. r... and Carl A. Harris, Philadelphia, Pa assignors to,8tandard Oil Development Company, a corporation oi! Delaware {N Drawing. Application August 12, m2. Serial No. 454,550

This invention relates to stabilized fined hydrocarbon oils of light lubricating oil consistency commonly termed white oils, particular grades of which are employed as medicinal oils. This application is a continuation-in-part of our co-pending application, Serial No. 293,950, filed September 8, 1939, which has matured into Patent 2,311,505 on February 16, 1943.

,The hydrocarbon base oils of the compositions prepared according to the invention are obtained by highly refining petroleum distillates of light lubricating oil consistency by means of treatment with successive volumes of fuming sulfuric acid followed by neutralization, washing and generally percolating or contacting with clay. The oils refined in this manner have colors of at least 30+ Saybolt. They consist largely of parafiln and naphthene hydrocarbons andthey have viscosities of above about 32 Saybolt-Universal seconds at 100 F. and preferably between about'55 and 350 seconds Saybolt Universal at 100 F. The

oils so prepared, are suitable as medicinal oils and are refined so as to pass the specifications for petrolatum liquidum'fU. S. P. 1

These highly refined oils are usually somewhat chemically unstable. oftentimes the oils develop objectionable odors and tastes. Also, such high- 1y treated oils upon exposure at elevated temperatures to metals, such as copper, cause staining of the metal. These effects appear to be connected withand are due presumably to the presence of unstable sulfur compounds formed by the interaction of concentrated sulfuric acid and certain organic compounds in the oils, particularly in those 'oils'oi Mid-Continent and Gulf Coast origins. These organic compounds are apparently present in traces and may also be introduced by contamination during handling the distillate in refineries making fuel oil and other low grade products. A test known as the copper strip test devised to indicate such instability is that of maintaining the oil at about 210 F. for about 2 hours in the presence of a highly polished copper strip: any tarnishing or discoloration is considered as-evidence of instability. The ence 0t sulfur is readily demonstrated by removing the copper stain with nitric acid and testing for sulfates with barium chloride.

It was disclosed in our co-pendlng'application. Serial No. 293,950, that the non-volatile, oil-soluble, relatively water insoluble, organic compounds pres- 4 mm (CL 252-42) highly re- The acid from this test usually takes on color factory addition agents to white oils in that they have suitable oil solubility and they do not impart a detectable taste to the composites in the concentrations in which they are used. Also, the

compounds employed are relatively inexpensive and are added to the oils in very low concentrations. The present invention is an'extension of the use of certain compounds of this class. namely, the mono-hydroxy aromatic carboxylic acids. These compounds are particularly effective as stabilizing agentsfor mineral white oils .dlficult to correct by other compounds added as inhibitors or even by reprecessing in one form or another.

It has now been found that all mineral white oils are not equally responsive to correction of their instability characteristics by the addition of the inhibitory compounds disclosed in our copending application, Serial No. 293,950. It was stated in that prior application that one of the tests to which finished oils are subjected is the hot acid test as described in the U. S. Pharmacopoeia (9th edition, page 315) In this test the finished oil-resists the action of hot concentrated acid as shown by shaking together equal quantities of the oil and sulfuric acid at C.

provement. Normally th hot acid test is employed as a control to indicate sufilciency of treat= ment. I

It has been known for some time that there are some m-called technical white oils, 1. e., oils of 30+ Saybolt but oi low hot acid testwhich do not pass the, copper test and which are not I made to pass the copper testby the addition of the inhibitor compounds commonly employed in white oil manufacture. It has now been found that when these technical white oils are given a further treatment withconcentrated sulfuric acid and resultant productsfinished to give a U. S. P. hot acid test, then the instabilities of such added treated oils are readily corrected by the addition of from 0.01% to 0.00005% of a monohydroxy aromatic carboxylic acid. These compounds may be added directly to' the oil or dissolved in aof acidic characteristics andof molecular weight above about may be added to these hi h y refined oils to combat the chemical lnstability. It was found that these compounds were satissmall amount of oil to make a concentrate, which is employed i or blending into the oil.

Or the monohydro aromatic carboxylic acids suitable as inhibitors in white 0115, it has been found particularly advantageous to employ salicylic acid or the alkylated salicylic acids. These alkylated salicylic acids are more soluble in oil than salicylic acid itself and, therefore, blend much more readily and easily with the oil. The salicylic acid as a group are also colorless and free from odor and do not impart color or thermal instability in the mineral oil composites. Worthy orparticular mention among th salicylic acids as being effective in concentrations of from 0.00005% to 0.01% of concentration are the following compounds and their respective solubilities in 100 grams of 55 Saybolt Viscosity at 100 F. mineral white oil:

. Grams Salicylic acid .6328 Tertiary butyl salicylic acid .532 Tertiary amyl 2 Thymotic acid (methyl, isopropyl salicylic acid) I 1.105

It would seem that the monohydroxy arc- 'matic carboxylic acids are unique as corrective tive as salicylic acid; Beta resorcylic acid (di- 3 hydroay benzoic acid) and gallic acid (trihydroiw benzoic acid) were found to have little or no efiect on the copper test. The eflfects oi. the various compounds in mineral oils of 90 Viscosity Saybolt at 100 F. containing the various compounds when subjected to the copper test are shown in the folio tabulation:

Amount Copper added test Percent Unblcuded oil Not. pass. Salicylic:

(Orliydroxy benzoic) 0031 Pam. M-hy 0901 Not pass.

-hydroxy be 001 Pass. P-hydroxy benzoim- 0001 Not pass. P-hydrory 001 Pass. Beta resorcylic acid 0001 Not pass 001 Do. 01 Do. Gallic acid- 0901 Do. 001 Do. 01 Do The particular efiectiveness of the monohy I droxy aromatic carbomlic acids as inhibitors in finishedoils which have been treatedwith suificient fuming sulphuric acid to pass the U. S. P. hot acid test by a practical margin appears connected with the removal, modification or stabilization of the unstable sulfur compounds previously produced in the oil as a result of the treatment with sulfuric acid of certain stocks. This opinion is supported by the observation that the staining which the inhibited oils cause upon .copper strip at 210 F. is usually due to the formation of copper sulfide. No definite reason can be advanced for the formation of such unstable sulfur compounds-in some stools and the lack of formation of such compounds in other cases. The higher grade of parailinic stock for example show little tendency to the formation of these compounds but they may be present in these oils as a result of contamination in their handling through pipe lines and tankage. Mid- Continent and-Coastal base stocks on the other hand often show the instability and it would appear in these cases that lt is connected with impurities in the base stock or formed during distillation, and then subsequently reactive with sulfuric acid during the final refining stages.-

The invention is'not to be limited to the use of the particular compounds shown nor to any theory with regard to the activity of the ingreclients but only to the following claims in which it is desired to claim all the novelty inherent in the invention. What is claimed is:

l. The method of stabilizing highly refined mineral white oils which comprises incorpothe said white mineral oil has a viscon'ty between about 55 and 350 Saybolt-Universal seconds at 3. The method of stabilizing highly refined mineral white oil according to claim 1 in which the .monohydroxy aromatic carboxylic acid is a salicylic acid.

i. The method of stabilizing highly refined mineral white oil according to claim 1 in which 5 the monohydroxy aromatic carboxylic acid is an alkylated salicylic acid. 

